I. Field of the Invention
The present invention relates generally to light sensitive control means and more particularly to photodetection means adapted to detect the presence of an object in proximity thereto. Specifically, the invention is concerned with an ambient light compensating circuit which allows the photodetection means to effectively operate in variable ambient light conditions.
II. Description of the Prior Art
Photoelectric control circuits having means for compensating for variations in lighting conditions are well known in the art and include those shown in U.S. Pat. No. 3,089,065 to L. E. Worden U.S. Pat. No. 3,328,590 to C. B. Kapsambelis, U.S. Pat. No. 3,811,046 to H. Levick, U.S. Pat. No. 3,586,445 to J. H. Martin, Jr., and U.S. Pat. No. 3,867,628 to R. M. Brown.
Typical ambient light compensating circuitry, as disclosed in Kapsambelis, conventionally requires relatively complex circuitry, as evidenced by functional blocks 24, 12, 14, and 16 shown in FIG. 1 of Kapsambelis. The necessity for this complex circuitry, with its attendant cost and unreliability, has made the use of such ambient light compensating circuitry impractical in many instances.
Other prior art ambient light compensating circuitry, as typically disclosed by Levick, uses a capacitor voltage level to compensate for variations in the ambient light. The use of such a capacitor materially reduces the response time of the ambient light compensating circuit to variations in ambient light and therefore limits its application.
There is, therefore, a need for an ambient light compensating means which is relatively simple, reliable, inexpensive, and which has a relatively fast response time to changes in ambient light conditions.
The present invention solves this need by providing a very simple ambient light compensating means utilizing a minimum of components with the accompanying improvements in cost and reliability. Further, the ambient light compensating means provided has a relatively fast response time to variations in ambient light and is readily adaptable to existing light sensing circuits.